Aegyptianella ranarum sp. n. (Rickettsiales, Anaplasmataceae) was recorded from bullfrogs (Rana catesbeiana Shaw), green frogs (Rana clamitans Latreille) and mink frogs (Rana septentrionalis Baird) from five sites in southern Ontario. The rickettsia occurs within membrane bound vacuoles in the cytoplasm of erythrocytes with up to 120 organisms in mature inclusions. The pattern of replication of A. ranarum in host erythrocytes and its prevalence over a 3-yr period in frogs from Algonquin Park, Ontario are discussed.